I have serious concerns about an instructor who says practice more without giving proper guidance. There is a possibility of serious injury in any break fall if not done correctly and telling a student to figure it out on your own in my opinion is gross negligence.
In one of the old Aikido Journal there was a break down on serious injuries in Aikido in Japan. Some were the result of repeatedly falling poorly. The students suffered from headaches to paralysis to death.

Teachers should never just tell students they need more practice with out giving corrections or telling them to stop completely if a student may hurt themselves.

Assuming a little too much, I feel. He's been told he needs to practise more, which he does. Nothing there to indicate he's been told that and left to get on with it and injure himself.

The article in AJ, IIRC, talked about deaths due to excessive training as a kind of hazing, not poor ukemi.